According to U.S. Pat. No. 3,509,032, 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimide are obtained by chlorination of 3-dimethylaminopropionitrile with Cl.sub.2 with irradiation by UV light, it being necessary for the temperature of the chlorination to sometimes be above 150.degree. C., in particular from 180 to 220.degree. C., in order to permit the desired products to form (see column 2, line 51 to 53 and Example 2 and 3). Such high chlorination temperatures are, however, disadvantageous when carrying out the procedure industrially.
According to DE-A 3 900 917, 4,5,6-trichloropyrimidine is prepared from the hydrochloride of 3-dimethylarninopropionitrile in a single-step chlorination at a temperature of from 120 to 130.degree. C. However, some aspects of this procedure can still be improved upon, in particular as regards its suitability for large-scale batches.
Furthermore, most of the processes described in the prior art have the disadvantage that during subsequent distillation insoluble distillation residues are formed, which can only be removed from the distillation vessels at considerable expense. In addition, the resulting products gas very severely during distillation.
The object of the present invention was therefore to provide a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidines starting from 3-dimethylaminopropionitrile which does not have the above disadvantages.